The need for cooling has increased in various applications due to higher heat flux densities resulting from newly developed electronic devices, being, for example, more compact and/or higher power than traditional devices. Examples of such improved devices include, for example, higher power semiconductor light-sources, such as lasers or light-emitting diodes, RF power devices and higher performance micro-processors, hard disk drives, optical drives like CDR, DVD and Blue ray drives, and large-area devices such as flat TVs and luminaires.
As an alternative to cooling by fans, document US 2006/0237171 discloses a jet generating device comprising a vibrating member and a housing having a nozzle and a first chamber containing the gas. The jet generating device discharges the gas through the nozzle as a result of driving the vibrating member thereby enabling cooling of a heat sink. The housing may also comprise a second chamber also having a nozzle. In this case, when air is discharged from the nozzles, sound is generated independently from the nozzle associated with the first chamber and the nozzle associated with the second chamber. Since the sound waves that are generated at the nozzles have opposite phases, the sound waves weaken each other. This makes it possible to further reduce noise. It is desirable that the volumes of the first and second chambers are the same. This causes the amount of air that is discharged to be the same, so that noise is further reduced.
However, a drawback with previously proposed systems, e.g. as disclosed in US 2006/0237171, is that they require subsonic frequencies or mechanical symmetry to achieve satisfactory noise reduction. This limits the range of applications as there often are inherent mechanical.